Overview on Welding Fixtures, Welding Joints, Welding Defects and CO2 arc welding

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Overview on Welding Fixtures, Welding Joints, Welding Defects and
CO2 arc welding
Rupesh Desale1, Sandesh Donapurge2, Sushant Bhor3, Ved Bhalerao4, Prof. Madan Kulkarni5
B.E. Student1,2,3,4, Assistant Professor5
Department of Mechanical Engineering
Nutan Maharashtra Institute of Engineering and Technology, Talegaon Dabhade, Maharashtra, India
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Abstract: This paper is an over view of the commonly used
welding joint’s while welding any workpiece. Also, the fixture
used, to position the workpiece while welding is discussed.
While welding while welding many irregularities, poor weld,
imperfections are formed and are classified in manytypes. The
types of welding defects are also part of this paper along with
their detection process. And one of the important welding
processes i.e. CO2 arc welding process, the welding in which a
consumable filler material used and is used to get deep
penetrations while welding, is discussed. Now, different
welding conditions have different effects on the weld, this
welding conditions can be the metal being welded,
forehand/backhand welding, welding velocity, etc.
Keywords: arc-welding, defects, fixtures, joints,
welding, CO2 arc Welding, conditions
1. Introduction:
Welding is a fabrication process where two or more parts
are fused together by applyingveryhighheatandsometimes
pressure.
Welding is most important and essential process in
industrial world. CO2 Welding is commonly used in
automobile industry, construction industry, fabrication
industry, aviation industry, etc.
2. Common Welding Fixtures
2.1 Gas Welding Fixture
In Gas Welding process is done by using the heat flame
caused by a reaction of oxygen and fuel gas, metals are
melted and joined together. For gas welding if the loss of
heat is too rapid the weld will develop many cracks. To
provide enough support to weldment, large masses of the
fixture are kept away from the welding point.
2.2 Arc Welding Fixture
In arc welding in which electricity is used to create a high
temperature for welding, Temperatureishigherthanthegas
welding. The fixture used in arc welding should apply
enough force to firmly hold the workpiece, also it should
easily dissipate heat. And this fixture should also provide
proper alignment as well as support to the work piece.
2.3 Resistance Welding Fixture
For Resistance welding mainly two types of fixture are used
first is the combined unit of both machine and the fixture.
And second is the fixture to specific weldingmachineswitha
single electrode. Insulation plays an important role for
fixtures here, all the magnetics, especially ferrous materials
should be kept away from the welding machine, and the
fixture should be made of non-magnetic materials.
2.4 Laser Welding Fixture
In laser welding a high intensity laser beam is incident,
where the welding is needed, this melts the material and
thus joins the elements. It is most popularlyusedwherehigh
precision is needed. The fixture should be made such that it
prevents the vibration, also height should be maintained
properly. And also, there should be sufficient space between
the workpiece and other parts to be welded.
3. Some special types of fixture used for specified
purposes:
3.1 Welding Fixture for Air filters in automobiles
Air Filters used in automobiles have two fans which need to
be welded onto the shell of the filter.Thefixtureusedhelpsto
maintain the eccentricity, height and angle. It has a lower
base, supported with four rod this table has a central rod to
hold the fan in proper position and also an arrangement
made to hold the shell in proper position to maintain the
eccentricity. Modeling of fixturesisdoneusingCreosoftware.
This fixture is economical, easy to use, work, has high degree
of accuracy, time of operation is reduced.
3.2 Welding Fixture with Active Position
Adapting Functions
In today’s fast-moving world robotic welding is commonly
used. The fixture used for robotic welding needs to be
accurate, this will increase the efficiency and quality. This

fixture base can tilt rotate along x-axis, can do translation
movement and allow rotate along z-axis in relation with
slider. The worktable is of hexagonal shape. Also has rack
and pinion arrangement along with adjustable clamping to
hold the work piece. This fixture helps in clamping
workpieces of various sizes and geometries.
3.3 Fixture for the Footrest Stand Component
The fixture is used for the footrest stand, where the
component is to be located with high accuracy. This fixture
has a rest plate, which has three pins to restrict the
movement of the workpiece. There are few locating pads
which are used to align and locate the component andfix the
bushes accurately. First the bushes are placed accurately
using clamps and then are welded round and welded
accordingly. Once the welding operation is done, the clamps
of the fixture will get detached. Solid works modeling
software is used for modeling.
3.4 Fixture for motor case assembly
The motor case is approximately 4m long, it comprises 4
main parts i.e. 2 tubes, rear end and head. Also, some other
parts like brackets, clamps need to be mounted. So, fixture
design has high accuracy satisfying the above needs. The
fixture has a collapsible assembly and roller support
assembly to avoid the deflection of the tubes. Thefixturehas
a sequential setup to improve the quality. Also, clamps are
provided to achieve appropriate tolerance. The modeling
software used for designing elements is UNIGRAPHICS NX
8.0.
3.5 Welding Fixture for a Single Door Frame
The fixture used for the door frame should possess more
clinching power, and should hold the door frame rigidly.
Also, the clamping used for proper positioning should not
restrict the welding and should be easily removable once
welding is done. The fixture is made of a base plate and 2
rectangular blocks are mounted to hold each strip of the
door frame in rectangular positions. The strips are held
together (tightened) using cotters. Thefixtureisina slanting
position with respect to the surface to get proper welding
done. The fixture is portable and has many industrial
applications.
3.6 Fixture for Fuel Tank Mounting Bracket
The mounting of the fuel tank consists of 6 parts which are
needed to weld. The fixture used for the fuel tank mounting
bracket has a rotating plate mounted on a plumbing block
which helps to tilt the fixture by 45o, which is mounted on a
bearing housing which can rotate up to 180o in horizontal
direction. In this mounting the distance plays an important
role, so the fixture has locator pins to locate the distance, if
due to some technical issue the distanceisnotmaintained an
alarm gives the signal for the misalignment. Also, if there is
any misalignment in the bracket the welding torch does not
work. Thus, this fixture helps to maintain the quality and
accuracy of the mounting bracket.
4. Types Of Welding Joints
Welding Joint is referred to as joining or fitting of metal
surfaces in prior arrangement or configuration according to
requirement. Application of welding joints can be endless
because of its monopoly of use in the industry in today’s era.
According to AWS (American Welding Society) types of
welds are classified into 5 types:
1. Butt joint welding
2. Lap joint welding
3. Edge joint welding
4. Tee joint welding
5. Corner joint welding
4.1 Butt Joint Welding
Butt Joint Welding is a type of welding where two adjacent
surfaces are joined together. Application of Butt weldingisit
is used in pipes, fabrication of structures, valve fittings,
automotive parts etc.
Types of Butt Welding:
1. Square welding
2. Single bevel welding
3. Double bevel welding
4. V-groove welding
5. Double V-groove welding
6. U-groove welding
7. Double U-groove welding
8. J-welding welding
9. Double J-groove welding
Fig. 1: - Butt Joint Welding

4.2 Lap Joint Welding
Lap Joint Welding is a type of welding where the
overlapped metal surfaces are joined or fitted together. It
is widely used in combined electronbeam,laserbeam,and
resistance spot welding. Lap joints are often used on thick
materials, and are used for sheet metal.
Some drawbacks of lap joint welding are lamellar tearing
and corrosion due to the overlapping of fall metals. But
you can easily handle them by applying the correct
technique of modifying the variables
Following are the typical examples of lap joints.
1. Filet welding
2. Spot welding
3. Plug welding
4. Slot welding
5. Bevel groove welding
6. Flare bevel groove welding
7. J-groove welding
Fig. 2: - Lap Joint Welding Types
Fig. 3: - Lap Joint Welding
4.3 Edge Joint Welding
Similar to lap joint where the parallel surfaces are joined or
fixed together at the point of welding. It is often used for
joining the edges of sheet metal or mufflers. Used in areas
like low pressure and stress. It is not a very strong joint. The
defects in edge type welding are porosity, lack of fusion,lava
inclusion, etc.
Types of Edge Joint Welding:
1. V-groove welding
2 .U-groove welding
3 .J-groove welding
5. Square groove welding
6. Corner flange welding
7. Edge flange welding
Fig. 4: - Edge Joint Welding
4.4 Tee Joint Welding
In Tee Joint Welding, when the two metal plates are at
angle of 90° with one plate is lie on the center of the other
plate like a "T" shape. It is known as tee joint welding. But,
again we will have a drawback in the tee joint, which is
lamellar tearing. .
Following are examples of tee joint welding.
1.Plug welding
2.Slot welding
3.Bevel groove welding
4.Flare bevel groove welding
5.Fillet welding
6.J-groove welding
7.Melt through welding

3.5 Corner Joint Welding
Fig. 5: - Tee joint welding
Similar to tee type welding joint, the difference is the
positing of the metal surfaces in tee type the metals are
placed in the middle while in corner joint welding the metal
surface is placed at the corner end. Applications, of corner
joint welding are there are used in joining sheet metal
surfaces also used in manufacturing of boxes, frames, bars
etc.
Types of Corner Joint Welding:
1. Fillet welding
2. Spot welding
3. Edge welding
4. J-groove welding
5. U-groove welding
6. V-groove welding
7. Flare V-groove welding
8. Square or butt groove welding
9. Corner flange welding
Fig. 6:- Corner Joint Welding
5. Defects in Welding
Welding defects (flaw) are the unwanted irregularities
or discontinuities that are present in the welding
product, which is not acceptable under thestandardized
rules and regulations. Which later lead to wear and
failure of the weld and cause damage and loss to the
entire product or environment in which it’s been used.
According to American Society of Mechanical
Engineers (ASME) weld defect or flaw are caused due
to factors
1. 45% poor process conditions.
2. 23% operator error.
3. 12% wrong technique.
4. 10% incorrect consumable (filler material/rod).
5. 5% Bad weld channel.
5.1 Welding defects are classified as
A. External Welding Defects.
a. Cracking
b. Porosity
c. Undercut
d. Overlap
e. Spatter
B. Internal Welding Defects.
a. Slag inclusion
b. Lack of fusion
c. Incomplete penetration
d. Shrinkage cavities
Fig. 7: - Welding Defects
Shielding gas also affects the quality and strength
of the weld, we mostly use Carbon dioxide.
As it is 1.5 times heavier than air and has a high
oxidizing potential. And it gives few defects.

6.Techniques to identify defects
6.1 Dye Penetration Test (DPT).
Dye penetration test is used toidentifyandlocatethesurface
in all non-porous and non-magnetic materials.
In this method first we need make the surfacecleanandthen
apply color dye on the weld surface with thehelpofspraying
or brushing, then the extra dye is removed and then we
apply the developer which helps us to clearly notice the
defects that are present on the weld.
Fig. 8: - Dye penetration test
6.2 Magnetic particle inspection (MPI).
Magnetic particle inspection is a simple Non-destructive
testing to find irregularities and weld flaws in magnetic
materials.
In this method first, the specimen is passedthrough
an electric current to get a magnetic field or wecreateitwith
the help of an external magnetic field. And the edge of the
crack will be north and south poles now if present and we
sprinkle iron particles that are attracted to the crack edges
and we get to know the defects/flaws.
Fig. 9: - Magnetic particle inspection
6.3 Radiographic testing method (RT).
Radiographic testing method isNon-destructivetestingused
for the identification of internal defects or internal
discontinuities in the weld.
This method is based on short wavelength
electromagnetic radiation. Whichispassedthroughmaterial
and we get a radiographic film on the screen.
Fig. 10: - Dye penetration test
6.4 Ultrasonic Testing (UT).
Ultrasonic Testing method is Non-destructive testing used
for the thickness of the material and flaw detection.
In this method first we pass the high frequency
(0.5MHz to 20MHz) sound waves which travel through in
different speeds in different materials. The sound wave
signals are reflected back and then we get the results on the
screen and can know about the flaws.
Fig. 11: -Ultrasonic Testing

6.5 Visual Inspection (VI)
Visual Inspection is a Non-destructive examination method
mostly used for quality control, data analysis and checking
the correctness visually. In this method the Inspector whois
an experienced person of the field is there to take a closer
look and find out the flaws and defects of the weld.
7. CO2 Arc Welding
In CO2 arc welding, the filler welding wire is fed into the
welding torch with the help of a motor. To protect the
welding material from reacting with atmospheric oxygen
and nitrogen, CO2 gas is supplied from the nozzle to shield
the welding pool area.
Fig. 12: - CO2 Arc Welding
7.1 Principle of CO2 Arc Welding
The welded material having blowholes is not a good thing or
considered good. CO2 gas is decomposed by the high
temperature arc heat into CO and O near the arc. Now O in
FeO combines with Si and Mn and floats upon the surface of
the weld pool.
CO2 ⇆ CO + O
FeO + O ⇆ FeO
FeO + C ⇆ Fe + CO
FeO + Mn ⇄ Fe + MnO
2FeO + Si ⇆ 2Fe + SiO2
7.2 Molten Droplet Transfer: -
The process of melting a feeding wire and passing it to the
base metal can be done in three different ways i.e. short-
circuiting transfer, globule transfer and spray transfer.
7.3 Short Circuit Transfer
If a low welding current is used in CO2 arc welding or MIG
welding, the droplets are transferred to the base metal after
short-circuiting with it. It is suited for welding thin plates
and in all-position welding such as vertical or overhead
welding.
7.4 Globule Transfer
In high current CO2 arc welding, the mode of droplet
transfer becomes globule transfer mode. In this, a slightly
higher amount of spatter is emitted than in othermodes. But
it is used as it is highly efficient.
7.5 Spray Transfer
MIG welding uses DC electrode with inert gas shielding and
positive polarity, which leads to formation of small droplets
than the wire diameter due to the effect of plasma flow. This
means the emission of spatter is little and the weld bead
with a good appearance can be obtained.
8. Welding Conditions and Their Effects
8.1 When welding speed is increased
1. Penetration becomes less dip
2. Spatter increases
3. Undercut happens if speed is excessive
4. High welding reinforcement is required
5. Bead becomes less wide and narrower
8.2 Tip to Base Contact length is more
1. Staggered bead appearance
2. When feed rate is constant welding current
decreases and the penetration decreases
8.3 Long Nozzle Standoff
1. As the gas shielding effect reduces the porosity
increases
8.4 Short Nozzle Standoff
2. The splatter tends to block the nozzle and welding
quality decreases
3. We can’t see the line of welding as the nozzle is too
close to the line
8.5 High Welding Current
1. More deep penetration than normal
2. Higher weld reinforcement
3. Wider bead width
8.6 Welding torch inclined for forward welding
1. Bead width increases
2. Less penetration

3. Higher reinforcement is required
8.7 Shielding Gas
1. When the flow rate is low or high winds are flowing
porosity occurs
2. Its composition affects the properties of the weld
8.8 Base Metal Surface
1. Contaminants will damage the quality of the weld
and cause porosity
9. Features of Forehand Welding
1. We can easily target the feeding wire on the welding
line
2. Less reinforcement and flat bead shape is achieved
3. Consistent melting is achieved through the root
pass bead
4. As molten metal flows ahead shallow penetrationis
achieved
10. Features of Backhand Welding
1. As welding nozzle hides the line to be welded,
welding is a little difficult
2. High reinforcement and narrow bead shape is
achieved
3. It is hard to obtain consistent melting through the
root pass
4. As the molten pool is formed backwards deep
penetration is achieved
11. Influence of wind velocity
X-ray tests have shownthatthereisa sharpincrease
of blowholes when the wind is over 2 m/sec. in velocity and
the weld bead is deposited on a 9 mm thick plate.
12. Weld Imperfection and Preventive Measures
12.1 Pits or Blowholes
1. CO2 gas flow shortage
2. The gas heater is not working properly
3. CO2 gas is not pure enough
4. Gas shielding is not proper
12.2 Overlap
1. Welding current is too low
2. Welding current is too high
3. Too low arc voltage or welding speed
4. Welding wire is targeting the wrong position
12.3 Undercut
1. Welding current is too high
1. Voltage is too high
2. Welding speed is too high
3. There is rough manipulation of the welding torch
12.4 Meandered Bead
1. There is a deviation in the center of the wire fees
roller
2. The contact tip is loosened
3. Wire straightener is not adjusted properly
12.5 Inadequate Penetration
1. Welding current is too low
2. Arc voltage is too low or too high
3. Welding speed is too high
4. Welding wire is targeted in a wrong position
13. Conclusion
Thus, we have overviewed Welding Fixtures,
Welding Joints, Welding Defects and CO2 arc welding. also
analyzed about the parameters and properties affect
welding of joints and welding defects.
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